Rearview vision system for vehicle including panoramic view

ABSTRACT

A rearview vision system for a vehicle includes at least one image capture device directed rearwardly with respect to the direction of travel of the vehicle. A display system displays an image synthesized from output of the image capture device. The display system is preferably contiguous with the forward field of view of the vehicle driver at a focal length that is forward of the vehicle passenger compartment. A plurality of image capture devices may be provided and the display system displays a unitary image synthesized from outputs of the image capture devices which approximates a rearward-facing view from a single location. such as forward of the vehicle.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of patent applicationSer. No. 08/445,527 filed May 22, 1995, which is a continuation-in-partof patent application Ser. No. 08/023,918 filed Feb. 26, 1993.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to vision systems for vehiclesand, more particularly, to rearview vision systems which provide thevehicle operator with scenic information in the direction rearward ofthe vehicle. More particularly, the invention relates to a rearviewvision system utilizing image capture devices, such as CMOS imagingarrays and the like.

[0003] A long-felt need in the art of vehicle rearview vision systems isto reduce the amount of time spent gathering information of thecondition around the vehicle in order to safely carry out a vehiclemaneuver, such as a turn or a lane change. It has been determined thatup to about 50 percent of maneuver time is spent gathering informationwith conventional rearview mirrors. This typically requires viewing oneor more mirrors, turning the head and body to check blind spots, anddouble-checking the mirrors prior to executing the maneuver. Someimprovement has been obtained by adjusting mirror optics, for example,to increase the observed field of view rearward of the vehicle. However,this is achieved with an increase in image distortion which makes driverawareness of conditions to the side and rear of the vehicle even moredifficult.

[0004] Another long-felt need in the art of vehicle rearview visionsystems has been to eliminate exterior rearview mirrors by utilizingimage capture devices, such as cameras, in combination with dashboarddisplays. This would be beneficial because it would reduce wind drag onthe vehicle, wind noise and vehicle weight. Furthermore, rearviewmirrors protrude a substantial distance from the side of the vehicle,which makes maneuvering in tight spaces more difficult. Image capturedevices are capable of positioning in a greater variety of locations onthe vehicle, providing more flexibility of vehicle styling. It isfurther expected that camera systems would greatly reduce the blindspots to the sides and rear of the vehicle common with vehicles equippedwith conventional rearview mirror systems. The driver cannot perceivevehicles, objects, or other road users in such blind spots withoutturning his or her body, which interferes with forward-looking visualactivities.

[0005] Camera-based rearview vision systems for vehicles have notobtained commercial acceptance. One difficulty with proposed systems hasbeen that they present a large amount of visual information in a mannerwhich is difficult to comprehend. This difficulty arises from manyfactors. In order to significantly reduce blind spots, multiple imagecapture devices are typically positioned at various locations on thevehicle. The image of an object behind the equipped vehicle is usuallycaptured by more than one image capture device at a time and displayedin multiple images. This may confuse the driver as to whether more thanone object is present. When multiple image capture devices arepositioned at different longitudinal locations on the vehicle, objectsbehind the vehicle are at different distances from the image capturedevices. This results in different image sizes for the same object. Thiseffect is especially noticeable for laterally extending images, such asa bridge, highway crosswalk markings, the earth's horizon, and the like.Such images are at different vertical angles with respect to the imagecapture devices. This results in different vertical positions on thedisplay causing the elongated image to appear disjointed.

[0006] A camera system provides a monocular view of the scene, comparedto the binocular stereoscopic view obtained when the scene is viewedthrough a rearview mirror. This makes the ability to judge distances ina camera system a problem. This effect is most noticeable at distancesclose to the vehicle where stereoscopic imaging is relied uponextensively by the driver in judging relative locations of objects.Therefore, known camera systems fail to provide to the driver importantinformation where that information is most needed—at small separationdistances from surrounding objects.

[0007] Another difficulty with camera systems is that, in order toprovide a sufficient amount of information, the camera system typicallypresents the driver with a greatly increased field of view. Thisimproves performance by further reducing blind spots at the side andrear of the vehicle. However, an increased field of view is oftenobtained by utilizing a wide-angle lens which introduces distortion ofthe scene and further impairs the ability of the driver to judgedistances of objects displayed. The problem with such distortion of thescene is that the driver must concentrate more on the display and take alonger time to interpret and extract the necessary information. Thisfurther distracts the driver from the primary visual task of maintainingawareness of vehicles and other objects in the vicinity of the drivenvehicle.

[0008] Yet an additional difficulty with camera systems is that flatpanel displays present the image captured by the rearward-facing imagecapture device, or devices, at a focal length that approximates the armlength of the vehicle driver. In order to observe the condition of thevehicle utilizing the rearview vision system, the driver must change hisor her gaze from the forward field of view of the vehicle to thedisplay. Because the forward field of view of the vehicle is at a focallength that is much greater than the focal length of the displayedimage, the eyes of the driver must refocus upon changing gaze. Thisrefocusing further increases the amount of time for the driver toassimilate the information in the displayed image. Furthermore, when thegaze of the driver returns to the forward field of view, the eyes must,again, refocus to the greatly longer distance.

[0009] Yet an additional difficulty with camera systems is that offinding adequate space in the crowded area of the vehicle's dashboardfor the components making up the display.

SUMMARY OF THE INVENTION

[0010] The present invention is directed towards enhancing theinterpretation of visual information in a rearview vision system bypresenting information in a manner which does not require significantconcentration of the driver or present distractions to the driver. Thisis accomplished according to an aspect of the invention in a rearviewvision system having at least two image capture devices positioned onthe vehicle and directed generally rearwardly with respect to thedirection of travel of the vehicle. A display is provided for imagescaptured by the image capture devices. The display displays an imagesynthesized from outputs of the image capture devices which approximatesa rearward-facing view from a single location. In order to obtain all ofthe necessary information of activity, not only behind but also alongside of the vehicle, the virtual camera should be positioned forward ofthe driver. The image synthesized from the multiple image capturedevices may have a dead space which corresponds with the area occupiedby the vehicle. This dead space is useable by the driver's sense ofperspective in judging the location of vehicles behind and along side ofthe equipped vehicle.

[0011] The present invention provides techniques for synthesizing imagescaptured by individual, spatially separated, image capture devices intosuch ideal image, displayed on the display device. This may beaccomplished, according to an aspect of the invention, by providing atleast three image capture devices. At least two of the image capturedevices are side image capture devices mounted on opposite sides of thevehicle. At least one of the image capture devices is a center imagecapture device mounted laterally between the side image capture devices.A display system displays an image synthesized from outputs of the imagecapture devices. The displayed image includes an image portion from eachof the image capture devices. The image portion from the center imagecapture device is vertically compressed.

[0012] It has been discovered that such vertical compressionsubstantially eliminates distortion resulting from the spatialseparation between the cameras and can be readily accomplished. In anillustrated embodiment, the image compression is carried out by removingselective ones of the scan lines making up the image portion. A greaternumber of lines are removed further away from the vertical center of theimage.

[0013] The compression of the central image portion produces a deadspace in the displayed image which may be made to correspond with thearea that would be occupied by the vehicle in the view from the singlevirtual camera. Preferably, perspective lines are included at lateraledges of the dead space which are aligned with the direction of travelof the vehicle and, therefore, appear in parallel with lane markings.This provides visual clues to the driver's sense of perspective in orderto assist in judging distances of objects around the vehicle.

[0014] According to another aspect of the invention, image enhancementmeans are provided for enhancing the displayed image. Such means may bein the form of graphic overlays superimposed on the displayed image.Such graphic overlap may include indicia of the anticipated path oftravel of the vehicle which is useful in assisting the driver in guidingthe vehicle in reverse directions. Such graphic overlay may include adistance grid indicating distances behind the vehicle of objectsjuxtaposed with the grid.

[0015] According to yet an additional aspect of the invention, arearview vision system for a vehicle includes at least one image capturedevice positioned on the vehicle and directed generally rearwardly withrespect to the direction of travel of the vehicle. A display system isprovided which displays a rear image synthesized from an output of theimage capture device. The rear image is substantially contiguous withthe forward field of view of the vehicle driver and at a focal lengththat is forward of the vehicle passenger compartment and preferablywithin the depth of field of a vehicle driver viewing a distant object.Because the image has a focal length that more closely matches that ofthe forward field of view observed by the driver, the need for thedriver's eyes to refocus from the forward field of view to a muchshorter focus distance each time the gaze of the driver is directed atthe display system is minimized. This reduces the amount of timerequired for the driver to gaze at the displayed image and interpretobjects displayed in the image. Furthermore, the reduction in therepeated refocusing of the driver's eyes reduces driver fatigue. Ifthere are any near field objects in the periphery of the driver'sforward field of view, such as windshield wipers, windshield frame,dashboard, and the like, the display system is preferably positioned ina manner which blocks the view of such near field objects. In thismanner, the driver's gaze may shift between the forward field of viewand the long focal length display system without being refocused on thenear field objects. This is based upon a recognition that the driver'seyes will tend to refocus on the near field object momentarily eventhough the gaze is being redirected between the forward field of viewand the display system.

[0016] According to yet an additional aspect of the invention, arearview vision system for a vehicle includes at least one image capturedevice positioned on the vehicle and directed generally rearwardly withrespect to the direction of travel of the vehicle. A display system isprovided for displaying a rear image captured by the image capturedevice. The displayed image is a unitary image having an aspect ratiothat is between approximately 4:1 and approximately 2:1. In a mostpreferred embodiment, the image has an aspect ratio that isapproximately 8:3. The aspect ratio, according to this aspect of theinvention, is especially useful where the unitary image is synthesizedfrom a plurality of images which are captured by a plurality of imagecaptured devices and are tiled by the display device.

[0017] According to yet an additional aspect of the invention, arearview vision system for a vehicle includes a plurality of imagecapture devices positioned on the vehicle and directed generallyrearwardly with respect to the direction of travel of the vehicle. Adisplay system which includes at least one image generator and anoptical correction system is provided which displays an imagesynthesized from outputs of the image capture devices as a unitaryimage. Alternatively, the display system may include a plurality ofimage generators, each associated with one or more of the image capturedevices and an optical correction system which amplifies imagesgenerated by the image generators and merges them into a unitary image.The optical correction system additionally increases the focal length,or lengths, of the image, or images, generated by the image generator,or generators. The display system may be an opaque projection displaywhich is positioned approximately at the driver's arm length in front ofthe driver. Alternatively, the display system may be a view-throughheads-up display which projects the unitary image onto a combiner inorder to combine the unitary image with the forward field of view of thedriver.

[0018] These and other objects, advantages, and features of thisinvention will become apparent by review of the following specificationin conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a top plan view of a vehicle having a rearview visionsystem according to the invention;

[0020]FIG. 2 is a side elevation of the vehicle in FIG. 1;

[0021]FIG. 3 is a front elevation of a display according to theinvention;

[0022]FIG. 4 is the same view as FIG. 1 illustrating an alternativeembodiment of the invention;

[0023]FIG. 5 is a block diagram of an electronic system according to theinvention;

[0024]FIG. 6 is the same view as FIG. 3 illustrating an alternate modeof operation of the system;

[0025]FIG. 7 is the same view as FIG. 2 illustrating an alternativeembodiment of the invention;

[0026]FIG. 8 is the same view as FIG. 3 illustrating an alternativeembodiment of the invention;

[0027]FIG. 9 is the same view as FIGS. 1 and 4 illustrating analternative embodiment of the invention;

[0028]FIG. 10 is the same view as FIGS. 3 and 8 illustrating analternative embodiment of the invention;

[0029]FIG. 11 is a chart illustrating the horizontal row of pixels (n1,n2) on which an object will be imaged from two longitudinally separatedimage capture devices as that object is spaced at different longitudinaldistances from the image capture devices;

[0030]FIG. 12 is a forward elevation of a vehicle passenger compartmentas viewed by a vehicle driver;

[0031]FIG. 13 is a sectional view taken along the lines XIII-XIII inFIG. 12;

[0032]FIG. 14 is a sectional view taken along the lines XIV-XIV in FIG.12;

[0033]FIG. 15 is the same view as FIG. 14 of an alternative embodiment;

[0034]FIG. 16 is the same view as FIG. 14 of another alternativeembodiment;

[0035]FIG. 17 is an enlarged view of the display system in FIG. 14illustrating details thereof;

[0036]FIG. 18 is a block diagram similar to FIG. 5 of an alternativeembodiment of the invention;

[0037]FIG. 19 is a side elevation similar to FIG. 2 of an alternativeembodiment of the invention;

[0038]FIG. 20 is an enlarged side elevation of an image capture devicewith portions of the housing removed in order to reveal internalstructure thereof;

[0039]FIG. 21 is a block diagram similar to FIG. 5 of anotheralternative embodiment of the invention;

[0040]FIG. 22 is a block diagram similar to FIG. 5 of anotheralternative embodiment of the invention;

[0041]FIG. 23 is a block diagram similar to FIG. 5 of anotheralternative embodiment of the invention;

[0042]FIG. 24 is a block diagram similar to FIG. 5 of anotheralternative embodiment of the invention; and

[0043]FIG. 25 is a block diagram of a rearview vision system havingextended dynamic range capabilities.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0044] Referring now specifically to the drawings, and the illustrativeembodiments depicted therein, a vehicle 10, which may be an automobile,a light truck, a sport utility vehicle, a van, a bus, a large truck, orthe like includes a rearview vision system, generally illustrated at 12,for providing a driver of the vehicle with a view rearwardly of thevehicle with respect to the direction of travel T of the vehicle (FIG.1). Vision system 12 includes at least two side image capture devices 14positioned, respectively, on opposite sides of vehicle 10 and a centerimage capture device 16 positioned on the lateral centerline of thevehicle. All of the image capture devices are directed generallyrearwardly of the vehicle. Rearview vision system 12 additionallyincludes an image processor 18 for receiving data signals from imagecapture devices 14, 16 and synthesizing, from the data signals, acomposite image 42 which is displayed on a display 20.

[0045] As will be set forth in more detail below, the images captured byimage capture devices 14, 16 are juxtaposed on display 20 by imageprocessor 18 in a manner which approximates the view from a singlevirtual image capture device positioned forwardly of the vehicle at alocation C and facing rearwardly of the vehicle, with the vehicle beingtransparent to the view of the virtual image capture device. Visionsystem 12 provides a substantially seamless panoramic view rearwardly ofthe vehicle without duplicate or redundant images of objects.Furthermore, elongated, laterally-extending, objects, such as theearth's horizon, appear uniform and straight across the entire displayedimage. The displayed image provides a sense of perspective, whichenhances the ability of the driver to judge location and speed ofadjacent trailing vehicles.

[0046] Each of side image capture devices 14 has a field of view 22 andis aimed rearwardly with respect to the vehicle about an axis 24 whichis at an angle, with respect to the vehicle, that is half of thehorizontal field of view of the image capture device. In this manner,each of the image capture devices 14 covers an area bounded by the sideof the vehicle and extending outwardly at an angle defined by thehorizontal field of view of the respective side image capture device.Center image capture device 16 has a horizontal field of view 26, whichis symmetrical about the longitudinal axis of the vehicle. The field ofview of each side image capture device 14 intersect the field of view ofcenter image capture device 16 at a point P which is located a distanceQ behind vehicle 10.

[0047] Rear blind zones 30 are located symmetrically behind vehicle 10extending from the rear of the vehicle to point P. Side blind zones 25located laterally on respective sides of the vehicle extend rearwardlyof the forward field of view 36 of the driver to the field of view 22 ofthe respective side image capture device 14. An object will not becaptured by side image capture devices 14 or center image capture device16 if the object is entirely within one of the blind zones 25, 30. Inorder for an object, such as another vehicle V or other road usertravelling to the side of vehicle 10, to be observed by an operator ofvehicle 10, the object must be either at least partially within theforward field of view 36 of the driver or be captured by image capturedevices 14, 16 and displayed on display 20. FIG. 4 illustrates vehicle10 travelling on a three-lane highway having lanes L1, L2, and L3 withthe vehicle in lane L2. Another vehicle V is shown positioned mostlywithin one of the blind zones 25, but with the rearmost portion of thevehicle V extending into field of view 22 where the vehicle image willbe captured by one of side image capture devices 14. In the illustratedembodiment, vehicle V is a motorcycle travelling in the center of lanesL1 or L3 and represents a worst case for observing a vehicle travellingat least partially within one of the blind zones 25. In order for aportion of vehicle V to be extending either forwardly or rearwardly ofthe respective blind zone 25, where the vehicle V may be observed byeither the forward field of view 36 of the driver or by the rearviewvision system 12, the field of view 22 of side image capture devices 14must be sufficiently wide to capture a portion of vehicle V asillustrated in FIG. 4. Preferably, the horizontal field of view 22 ofside image capture devices 14 is no greater than that required toprovide sufficient coverage which would be in the range of betweenapproximately 55 degrees and approximately 70 degrees. In theillustrated embodiment, the horizontal field of view 22 is 61 degrees.In order for a portion of vehicle V to be within a vertical field ofview 40 of one of side image capture devices 14, the field of viewshould extend to the pavement at a plane M which intersects vehicle V(FIG. 2). Preferably, vertical field of view 40 is between approximately60 degrees and approximately 75 degrees. In the illustrated embodiment,vertical field of view 40 is 66 degrees.

[0048] A left overlap zone 32 and a right overlap zone 34 extendrearward from respective points P where the horizontal fields of view ofthe side image capture devices intersect the field of view of centerimage capture device 16. Overlap zones 32, 34 define areas within whichan object will be captured both by center image capture device 16 andone of the side image capture devices 14. An object in an overlap zone32, 34 will appear on display 20 in multiple image portions in aredundant or duplicative fashion. In order to avoid the presentation ofredundant information to the driver, and thereby avoid confusion andsimplify the task of extracting information from the multiple images orcombined images on display 20, the object should avoid overlapping zones32, 34. In practice, this may be accomplished to a satisfactory extentby moving points P away from the vehicle and thereby increasing distanceQ. It is desirable to increase distance Q to a length that will excludevehicles travelling at a typical separation distance behind vehicle 10from overlapping zones 32, 34. This separation distance is usually afunction of the speed at which the vehicles on the highway aretravelling. Therefore, optionally, distance Q may be made variable, notfixed. In such embodiment, the faster the vehicles are travelling, thefurther Q should be moved behind vehicle 10 to keep overlap zones 32 and34 outside of the recommended vehicle spacing. If, however, the vehiclesare travelling at a slower speed, then the generally acceptedrecommendation for vehicle spacing decreases and it is more likely thata vehicle will be within overlap zone 32, 34. Therefore, the distance Qmay be selected to accommodate expected vehicle spacing for an averagedriving speed of vehicle 10.

[0049] Distance Q is a function of the effective horizontal field ofview 26 of center image capture device 16. As field of view 26decreases, points P move further rearward of the vehicle from a distanceQ₁, to a distance Q₂, as best illustrated in FIG. 4. In order toincrease distance Q to eliminate redundant and duplicative informationdisplayed on display 20 for most driving conditions of vehicle 10, fieldof view 26 is preferably less than 12 degrees. In the illustratedembodiment, field of view 26 is between 6 and 8 degrees. Alternatively,distance Q may be dynamically adjusted according to some parameter, suchas the speed of vehicle 10. This would allow Q to be greater when thevehicle is travelling at a faster speed, where vehicle separation tendsto be larger, and vice versa. Field of view 26 may be adjusted byutilizing a selective presentation of pixels of the captured image inthe displayed image.

[0050] Referring to FIG. 3, image display device 20 displays a compositeimage 42 made up of a left image portion 44, a right image portion 46,and a center image portion 48. Each image portion 44-48 is reversed fromthe image as captured by the respective image capture device 14, 16utilizing conventional techniques. These techniques include reading theimage in reverse with the image capture device, writing the image inreverse to display device 20, or reversing the image in image processor18. Left image portion 44 is joined with central image portion 48 at aboundary 50. Central image portion 48 is joined with right image portion46 at a boundary 52. As may best be seen in FIG. 3, the image portionsat boundaries 50 and 52 are continuous whereby composite image 42 is aseamless panoramic view rearwardly of the vehicle. As also is apparentfrom FIG. 3, central image portion 48 is narrower than either left imageportion 44 or right image portion 46. This is a result of reducing thehorizontal field of view 26 of center image capture device 16sufficiently to move points P, and thus overlap zones 32 and 34, asufficient distance behind vehicle 10 to reduce redundant andduplicative images between image portions 4448. Composite image 42provides a clear image, which avoids confusion and simplifies the taskof extracting information from the multiple image portions 44-48. Asalso may be seen by reference to FIG. 3, display 20 may additionallyinclude indicia such as the readout of a compass 54, vehicle speed 56,turn signals 58, and the like as well as other graphical or videodisplays, such as a navigation display, a map display, and aforward-facing vision system. In this manner, rearview vision system 12may be a compass vision system or an information vision system.

[0051] In the embodiment of rearview vision system 12 having adynamically adjusted value of distance Q, the spacing between boundaries50 and 52 will dynamically adjust in sequence with the adjustment ofdistance Q. Thus, as overlap zones 32, 34 move further away from thevehicle; for example, in response to an increase in speed of thevehicle, boundary lines 50 and 52 will move closer together and viceversa. In this manner, composite image 42 is dynamic, having imageportions of dynamically adaptive sizes.

[0052] Display 20 is of a size to be as natural as possible to thedriver. This is a function of the size of the displayed image and thedistance between the display and the driver. Preferably, the displayedimage simulates an image reflected by a rearview mirror. As such, thesize of the displayed image is approximately the combined areas of thethree rearview mirrors (one interior mirror and two exterior mirrors)conventionally used with vehicles. As best seen by reference to FIGS. 2and 12, display 20 is preferably positioned within the driver'sphysiological field of view forward of the vehicle, generallyillustrated at 70, through the windshield 72 without significantlyobstructing the forward field of view. It is known that the driver'sfield of view, with the head and eyes fixed forward, extends further ina downward direction than in an upward direction. Display 20 could belocated above the field of view 70 wherein the display may be observedat the upward portion of the driver's field of view. However, theposition for the display illustrated in FIGS. 2 and 12 is preferredwherein the display is within the lower portion of the driver's field ofview.

[0053] Display 20 may be a direct view flat panel display, such as aback-lit or reflective liquid crystal display, a plasma display, a fieldemission display, a cathode ray tube electroluminescent, light-emittingdiode or deformable mirror display. The display may be mounted/attachedto the dashboard, facia or header, or to the windshield at a positionconventionally occupied by an interior rearview mirror. However, thesynthesized image could be displayed using other display techniques suchas to provide a projected or virtual image. Alternatively, a virtualimage may be displayed on an opaque display adjacent the forward fieldof view. Alternatively, a virtual image may be displayed on aview-through heads-up display in which the image is superimposed on theforward field of view.

[0054] In the embodiment illustrated in FIGS. 12-17, display 20 displaysan image at a focal length that is forward of the passenger compartmentof vehicle 10. Preferably, the image displayed by display 20 is at afocal length that is within the driver's normal depth of field whenviewing a distant object. Display 20 includes an image generator 74,which produces an image captured by one or more image capture devices14, 16, and an optical correction system 76, which increases the focaldistance of the image generated by image generator 74. In theillustrated embodiment, optic correction system 76 increases the focaldistance by collimating the rays, generally indicated at X, fromdiverging rays to generally parallel rays projected from the display.Optical correction system 76 additionally magnifies the image. In theillustrated embodiment, the magnification is a factor of two. In thismanner, optical corrective system 76 has the advantage of extending thefocal distance of the image generated by image generator 74 andenlarging the image by the factor of magnification thereof. Thisadvantageously allows each image generator 74 to project all or aportion of an image captured by one of image capture devices 14, 16, ora combination of portions of images from one or more image capturedevices, by tiling the images or image portions. This is accomplishedbecause the images projected from optical correction system 76 may abuteven though the corresponding image generators 74 do not. This providesa convenient technique for joining the images synthesized from the imagecapture devices into a unitary image which represents a panoramic viewrearward of the vehicle.

[0055] In the embodiment illustrated in FIG. 14, display 20 is an opaqueprojection display which projects the image directly toward the driver.In the embodiment illustrated in FIG. 15, a display device 120 is aview-through heads-up display in which the rays X are projectedgenerally upwardly by image generator 74 and optical correction system76 which are generally vertically aligned, or aligned forward ofvertical. The rays X are reflected off a first surface of windshield 72in the direction of the driver. Windshield 72 acts as a combiner whichcombines the image displayed by display 120 with a portion of theforward field of view 70 observed by the driver. In the embodimentillustrated in FIG. 15, a combiner other than the windshield may beused. Examples may be holographic or diffractive optical film elementsor beam splitters of metal or dielectric thin films. Furthermore, imageprocessor 18 may generate a line in the shape of a polygon, such as arectangle, around rear image 42. This provides a border around the imageto differentiate the rear view from the view forward of the vehicle.

[0056] In the embodiment illustrated in FIG. 16, display 20A is orientedat an angle with respect to the forward field of view of driver D. Imagerays X are reflected by a mirror 140 toward the driver. Display 20A isan opaque display, with mirror 140 blocking the driver's view of nearfield objects, such as wipers 98 and the like. Display 20A has theadvantage of being capable of location within a forward portion of thedashboard. Additionally, the only portion of the display visible to thedriver is mirror 140. This allows near field portions of the display tobe significantly reduced.

[0057] Because display 20 has a relatively long focus distance, display20 defines an observation cone, generally designated 78, within whichthe displayed image can be observed. Therefore, the head of the drivermust be properly oriented with respect to observation cone 78 in orderto allow the driver to observe the displayed image. However, driverscome in various sizes. Therefore, a driver may be too tall or too shortto have his or her head properly positioned within observation cone 78.In order to provide for various size drivers along with variousadjustments in seating positions and the like, an accommodation means,generally illustrated at 80, may be provided in order to accommodatevariations in the relationship between a driver's head and observationcone 78. In the illustrated embodiment, accomodation means 80 includesadjustment means 82 for adjusting the position of observation cone 78.The adjustment means may adjust the position of the observation coneeither vertically, horizontally, or both vertically and horizontally. Avertical adjustment means 82 is illustrated in FIG. 13 in which theadjustment means includes an electric actuator 84 which is joined bylinkage 86 with a portion of a housing 88 of display 20. Actuator 84 iselectrically interconnected through a reversing switch 90 with adriver-operated actuator 92 which may be positioned on dashboard 94 orother convenient position accessible to the driver. Housing 88 may beadjustably mounted, such as by a pivot 96, in order to allow housing 88to be adjustably repositioned with respect to dashboard 94. In thismanner, by operation of actuator 92, housing 88 may be pivoted upwardlyor downwardly with respect to pivot 96 in order to adjust the directionof observation cone 78. In this manner, the location of observation cone78 may be adjusted in order to coincide with the location of thedriver's head. In a similar fashion, the position of observation cone 78may be adjusted laterally, if desired. If a view-through heads-updisplay of the type illustrated in FIG. 15 is utilized, the position ofthe observation cone may be adjusted vertically and laterally, in asimilar manner, by mechanical or optical adjustments of display 20.

[0058] Accomodation means 80 may include extending the rearward field ofview displayed by display 20 laterally outwardly with respect to thebezel 89 beyond that normally observed by a driver. In this manner,.adriver's head located generally centrally within observation cone 78will observe a view generally rearwardly of the vehicle. As the driver'shead is moved laterally within observation cone 78, the driver willobserve images more laterally to the side of the vehicle as would occurif the driver's head were to be moved with respect to a conventionaloptical rearview mirror system.

[0059] Vehicle 10 may include one or more near field view objectsadjacent forward field of view 70. One such object is a windshield wiper98 of the vehicle. Other such objects may include the top of dashboard94, the frame around windshield 72, the hoodline, and the like. Thehousing of display 20 in FIG. 14 and mirror 140 in FIG. 15 arepositioned with respect to forward field of view 70 such that housing 88or mirror 140 covers any near field of view objects in the portion ofthe forward field of view adjacent display 20, 20A. In this manner, thegaze of the driver can switch between forward field of view 70 and theimage displayed on display 20, without the eyes of the driver focusingon any significant near field objects. This is based upon a discoverythat, even though the eyes of the driver are switching between the longfocal distance of the forward field of view and the long focal distanceof the image displayed by display 20, the eyes of the operator willunconsciously momentarily focus on any near field object positionedbetween the long focal distance views. Therefore, by blocking thedriver's gaze of any near field objects, the eyes of the driver will beless stimulated to refocus during the transition from field of view 70to display 20 and back again.

[0060] Image processor 18, which supplies a video signal 100 to imagegenerator 74, may have a second input 102 which modulates the intensitylevel of the image generated by image generator 74 and displayed bydisplay 20 (FIG. 14). The illumination level of the display is set inresponse to an ambient light input 104 which is an indication of theambient light level around vehicle 10. Image processor 18 responds tothe value of ambient light input 104 by producing a luminance intensitysignal 102 which increases the intensity of the display in response toincreases in ambient light level and decreases the intensity of thedisplay in response to decreases in ambient light level. However, thelevel of display luminance may be limited to vary between upper andlower limits such that, once ambient light reaches a particular upperlevel, further increases in ambient light level will not result in afurther increase in display intensity. Likewise, once the ambient lightlevel decreases below a particular value, further reductions in ambientlight level will not result in further reduction in display intensity.Ambient light input 104 may be produced by a separate ambient lightsensor of the type which produces a continuously variable output inresponse to variations in ambient light levels, in which case, theintensity of display 20 may be proportionately adjusted. Alternatively,ambient light input 104 may be produced by a vehicle headlight controlsystem (not shown) which switches the vehicle headlights on, or to anighttime condition, in response to decreases in ambient light levelsand switches the vehicle headlights off, or to a daytime running lightcondition, in response to increasing ambient light levels. Such systemis disclosed in commonly assigned U.S. patent application Ser. No.08/277,674 filed on Jul. 19, 1994, by Kenneth L. Schierbeek and Niall R.Lynam for an AUTOMATIC REARVIEW MIRROR SYSTEM WITH AUTOMATIC HEADLIGHTACTIVATION, the disclosure of which is hereby incorporated herein byreference. If the ambient light signal supplied to ambient light input104 is a binary signal representative of a daytime ambient light leveland a nighttime ambient light level, image processor 18 would typicallyprovide a signal on luminance intensity line 102 that would switch theintensity level of display 20 between two intensity levels.Alternatively, ambient light input 104 may be supplied with a signaldeveloped by one or more image capture devices 14, 16. The ambient lightsignal would be based upon an average intensity value sensed by all, ora group of, pixels in the image capture device or devices. Thisembodiment eliminates the necessity for a separate ambient light sensor.Alternatively, ambient light input 104 may be responsive to manualactuation of the vehicle's headlights by the driver. Additionally, acomfort level setting may be provided to allow the driver to adjust to apreferred brightness at one ambient light condition. Thereafter, thesystem automatically adjusts display brightness according to ambientlight changes.

[0061] In the illustrated embodiment, display 20 incorporates a combinedimage generator and optical correction system 106 which provides forboth image magnification and light ray collimation. In this manner, theimage projected from display 20 is larger than the image generated byimage generator 74 and has a focal length that is greater than theseparation distance between the image generator and the driver and,preferably, is generally at infinity (FIG. 17). Combined image generatorand an optical correction system 106 is disclosed in detail in U.S. Pat.No. 5,050,966 for an OPTICAL COMBINER COLLIMATING APPARATUS; 4,859,031for an OPTICAL COLLIMATING APPARATUS; 4,900,133 for a HEADS-UP DISPLAYCOMBINER UTILIZING A CHOLESTERIC LIQUID CRYSTAL ELEMENT; 4,987,410 for aMULTIPLE IMAGE FORMING APPARATUS; and 5,408,346 for an OPTICALCOLLIMATING DEVICE EMPLOYING CHOLESTERIC LIQUID CRYSTAL ANDNON-TRANSMISSIVE REFLECTOR, the disclosures of which are herebyincorporated herein by reference and will not be repeated. Suffice it tosay, combined image generator and optical correction system 106 includesa light source 108 which generates broad band white light which isgathered and reflected by a parabolic reflector 110. In the illustrativeembodiment, light source 108 is a tungsten halogen incandescent lamp.The light rays then pass through a dielectric green filter 112 whichpasses light in a specific region of the green portion of the spectrumand through a hot mirror 114 which removes the infrared content of thespectrum. Light then passes through a holographic diffuser 116 whichhomogenizes and shapes the light pattern. The light rays then passthrough a monochrome liquid crystal display with opposing linearpolarizers 118 which is supplied with a video signal by image processor18. Items 108-118 make up image generator 74, which, in the illustrativeembodiment, is a transmissive backlit liquid crystal display. However,image generator 74 could additionally be an emissive display or areflective display, all of which are well known in the art.

[0062] Light rays of the image generated by image generator 74 next passthrough an antireflective coated cover glass 120 which is joined with aleft-hand circular polarizer 122 which is bonded to this cover glass.The opposite surface of circular polarizer 122 is bonded to a lens 124having a 50/50 dielectric coating. Such dielectric coating allows lightrays to be both transmitted through the lens and reflected by the lens.The left-hand polarized light X′ transmitted through lens 124 contacts acholesteric liquid crystal layer (CLC) 126 which is left-hand polarized,which is what gives efficient reflection of left-hand polarized lightX′, as illustrated at X″. Fifty percent (50%) of light rays X″ getefficiently reflected by the 50/50 beam splitter on lens 124 asright-hand circular polarized light X″′. Right-hand polarized light X″′is transmitted by CLC layer 126 and passes through a right-hand circularpolarizer 128 and an anti-reflective coated cover glass 130.

[0063] As can be seen by reference to FIG. 17, the optical configurationof lens 124 in combination with the left-hand and right-hand circularpolarizers 122, 128 and cholesteric liquid crystal layer (CLC) 126,provide image magnification as well as collimate the image light inorder to produce a very long focal distance image. Advantageously, thisstructure allows image portions from multiple image capture devices tobe tiled into a unitary image. FIG. 17 illustrates an approach using asingle image generator. Merging of multiple image portions would requireadditional combined image generator and optical correction systems.Although image generators 74 for each of the image portions arelaterally spaced apart from each other, the amplification produced bycombined image generator and optical correction system 106 causes theimage portions to merge at their periphery. FIG. 17 illustrates anapproach using a single image generator. Merging of multiple imageportions would require additional combined image generators and opticalcorrection systems. Other optical elements such as prisms, or otherlenses, may be necessary to merge images to form a unitary image.Although the invention is illustrated with a combined image generatorand optical correction system using cholesteric liquid crystal opticalprocessing, other optical correction systems, as are known in the art,may be used. What is required is that the optical system generallycollimates the light generated by the image generator and, preferably,provides amplification to the generated image.

[0064] In the illustrated embodiment, rear image 42, synthesized fromthe output of image capture devices 14, 16, has a lateral width versesvertical height aspect ratio that is between approximately 4:1 and 2:1.Most preferably, the aspect ratio of image 42 is 8:3. This allows apanoramic view rearwardly of the vehicle with an optimum informationcontent while reducing display of irrelevant information. The aspectratio of display 20 may be different from that of the displayedsynthesized image 42. The remaining portion of the display, either aboveor below image 42, may be utilized to display images other thansynthesized image 42. For example, the remaining portion of the displaycan be used to display auxiliary information such as one or morevehicle-operating parameters, such as vehicle speed indicia 56, headingindicia 54, or turn signal indicia 58. Alternatively, the remainingportion of the display can be a reconfigurable high-information contentdisplay area to selectively display various types of information. Suchinformation may include incoming facsimile or pager information, phonenumbers, and navigational aids including pull-up maps, route guidanceinformation, global positioning system (GPS) data, intelligent vehiclehighway system (IVHS) information, as well as radio and environmentalsystem control settings, and the like. Display 20 is especially usefulfor displaying such alternative data. Because display 20 has a very longfocal length, the driver may consult the alternative data by switchingthe gaze of the driver between forward field of view 70 and to display20 which does not require extensive refocusing of the driver's eyes.This allows the driver to consult the alternative data quickly withreduced fatigue and distraction. The content of the auxiliaryinformation displayed may be user-selectable by a keypad, trackball, orother input device on the dashboard, steering column, or other positionreadily accessible to the driver.

[0065] Although various camera devices may be utilized for image capturedevices 14, 16, an electro-optic, pixilated imaging array, located inthe focal plane of an optical system, is preferred. Such imaging arrayallows the number of pixels to be selected to meet the requirements ofrearview vision system 12. The pixel requirements are related to theimaging aspect ratio of the respective image capture devices, which, inturn, are a function of the ratio of the vertical-to-horizontal field ofview of the devices, as is well known in the art. In the illustratedembodiment, the imaging aspect ratio of side image capture devices 14 is2:1 and the image aspect ratio of central image capture device 16 isvariable down to 0.1:1. Such aspect ratio will produce images which willnot typically match that of commercially available displays. Acommercially available display may be used, however, by leaving ahorizontal band of the display for displaying alpha-numeric data, suchas portions of an instrument cluster, compass display, or the like, asillustrated in FIG. 3.

[0066] In the illustrated embodiment, image capture devices 14, 16 areCMOS imaging arrays of the type manufactured by VLSI Vision Ltd. ofEdinburgh, Scotland, which are described in more detail in co-pendingUnited States patent application Serial No. 08/023,918 filed Feb. 26,1993, by Kenneth Schofield and Mark Larson for an AUTOMATIC REARVIEWMIRROR SYSTEM USING A PHOTOSENSOR ARRAY, the disclosure of which ishereby incorporated herein by reference. However, other pixilated focalplane image-array devices, which are sensitive to visible or invisibleelectromagnetic radiation, could be used. The devices could be sensitiveto either color or monochromatic visible radiation or near or farinfrared radiation of the type used in nightvision systems. Each imagecapture device could be a combination of different types of devices,such as one sensitive to visible radiation combined with one sensitiveto infrared radiation. Examples of other devices known in the artinclude charge couple devices and the like.

[0067] Preferably, image capture devices 14 and 16 are all mounted atthe same vertical height on vehicle 10, although compromise may berequired in order to accommodate styling features of the vehicle. Thehorizontal aim of image capture devices 14 and 16 is preferablyhorizontal. However, the portion of the image displayed is preferablybiased toward the downward portion of the captured image becausesignificantly less useful information is obtained above the horizontalposition of the image capture devices.

[0068] Each image-capturing device 14, 16 is controlled by appropriatesupporting electronics (not shown) located in the vicinity of theimaging array such that, when operating power is supplied, either ananalog or a digital data stream is generated on an output signal linesupplied to image processor 18. The support electronics may be providedpartially on the image chip and partially on associated electronicdevices. For each exposure period, a value indicative of the quantity oflight incident on each pixel of the imaging array during the exposureperiod is sequentially outputted in a predetermined sequence, typicallyrow-by-row. The sequence may conform to video signal standards whichsupport a direct view such that, when a scene is viewed by animage-capturing device, the image presented on a display representsdirectly the scene viewed by the image-capturing devices. However, whenlooking forward and observing a displayed image of a rearward scene, thedriver will interpret the image as if it were a reflection of the sceneas viewed through a mirror. Objects to the left and rearward of thevehicle, as viewed by the rearward-looking camera, are presented on theleft-hand side of the display and vice versa. If this reversal iseffected in image processor 18, it may be by the use of a data storagedevice, or buffer, capable of storing all of the pixel values from oneexposure period. The data is read out of the data storage device in areversed row sequence. Alternatively, the imaging array electronicscould be constructed to provide the above-described reversal at theimage-capturing device or at the display.

[0069] Data transmission between image capture devices 14, 16 and imageprocessor 18 and/or between image processor 18 and display 20 may be byelectrically conductive leads. The leads may comprise either a serial orparallel bus. Alternatively, the data transmission may be via plastic orglass fiber-optic cable or an RF link. It is possible, for particularapplications, to eliminate image processor 18 and direct drive display20 from image capture devices 14, 16 at the pixel level. This may beaccomplished by providing an interface between the output of imagecapture device 14, 16 and display 20 which synchronously maps imagepixels captured by the image capture device, or devices, to the display.This synchronous mapping may be accomplished by providing a one-to-onemapping in which each pixel measurement is communicated to the display.Alternatively, the interface may only transmit pixel data whichrepresents changes in the captured image. This allows for a reduction inthe communication bandwidth necessary to transmit data between the imagecapture device, or devices, and the display. This may be accomplished byencoding the pixel data which represents changes in the captured imagewith additional data which designates the position of the pixel or otherrelevant information. Communication between the image capture device, ordevices, may be multiplexed.

[0070] The data streams from image-capturing devices 14, 16 are combinedin image processor 18 and directly mapped to the pixel array of display20. This process is repeated preferably at a rate of at least 30 timesper second in order to present an essentially real time video image. Theimage captured by side image capture device 14 on the right side of thevehicle is presented in right image portion 46 and the image from sideimage capture device 14 on the left side of the vehicle is displayed onleft image portion 44. The image from center image capture device 16 isdisplayed on central image portion 48. The three image portions 44-48are presented in horizontal alignment and adjacent to each other.However, the composite image may be positioned at any desired verticalposition in the display 20. It is also possible to display imageportions 44-48 on separate image devices which are adjacent each other.

[0071] In vision system 12, side image capture devices 14 are positionedpreferably at a forward longitudinal position on vehicle 10 and centerimage capture device 16 is positioned at a rearward longitudinalposition on the vehicle. As best seen by reference to FIG. 7, thispositioning creates a difference in the vertical angle between each sideimage capture device 14 and center image capture device 16 with respectto a fixed location P₁ that is a distance D₁ behind the vehicle. Thisdifference in sensing angle will cause each side image capture device 14to image an object located at P₁ on a horizontal row of pixels that isdifferent from the horizontal row of pixels that center image capturedevice 16 will image the same object. If the image is below thehorizontal centerline of the image capture device, it will be imaged ona lower row of pixels by center image capture device 16 than the row ofpixels it will be imaged by the side image capture devices 14, asillustrated in FIG. 7. This mismatch between horizontal pixel rows ofthe captured image is furthermore a function of the distance of thecaptured image from the rear of the vehicle. This can be understood byreference to FIG. 11 which presents a chart 90 having a first column 92of pixel lines n1, measured from the array centerline, at which anobject will be imaged by side image capture device 14 and a secondcolumn 94 of pixel lines n2, measured from the array verticalcenterline, at which the same object will be imaged by center imagecapture device 16. The result is that an object, which is captured byboth side and center image capture devices 14, 16, will be verticallydisjointed at the boundary of the displayed image, if the object iscaptured by more than one image capture device. The amount ofdisjointment will be greater closer to the vehicle and less at furtherdistances. If the object is elongated in the horizontal direction, suchas earth's horizon, bridges, or cross-markings on highways, then theobject will appear to be either broken or crooked.

[0072] In order to provide uniform display of laterally elongatedimages, a rearview vision system 12′ is provided having a central imageportion 48′ which is processed differently from the image displayportions 44′ and 46′ produced by the side image capture devices (FIG.8). Central image portion 48′ is reduced vertically, or compressed, byremoving specified scan lines, or pixel rows, from the image captured bycenter image capture device 16 in a graduated fashion. The difference inthe pixel line at which an object will be imaged by each of the side andcenter image capture devices is a function of the distance D of theobject from the rear of the vehicle, with a greater variation occurringat shorter distances and the variation reducing to zero for infinitedistances. Therefore, the compression of central image portion 48′ isnon-linear, with substantially no compression at the vertical center ofthe image and greater compression at greater distances above and belowthe vertical center point of the image. This is accomplished by removingspecific lines from the center display in a graduated fashion with agreater number of lines removed further from the vertical center of theimage. The removed lines may be merely discarded in order to verticallyreduce the image. Alternatively, the data contained in the removed linesmay be utilized to modify the value of adjacent pixels above and belowthe removed line in order to enhance the quality of the compressedimage. Averaging, median filtering, or other such known techniques mayalso be used.

[0073] Each of right image portion 46′ and left image portion 44′includes an upper portion 64 which extends above the compressed upperportion of the central image portion 48′. In the illustrated embodiment,upper portions 64 are deleted in order to present a uniform upperhorizontal boundary for display 20′. In the illustrated embodiment, themismatch between the lower horizontal boundary of central image portion48′ and each of the left and right image portions provides a dead space66 which provides a visual prompt to the user of the approximatelocation of the rearward corners S of vehicle 10. This dead space 66 inthe image displayed on display 20′ approximates the footprint occupiedby vehicle 10 when viewed from point C. This is particularly usefulbecause it provides a visual indication to the driver that a vehiclepassing vehicle 10, as viewed in either left image portion 44′ or rightimage portion 46′, is at least partially adjacent vehicle 10 if theimage of the approaching vehicle is partially adjacent to dead space 66.

[0074] In an alternative embodiment, the vertical compression techniquemay be applied to only a lower vertical portion of central image portion48′. In most driving situations, objects imaged by rearward-facing imagecapture devices above the horizon are at a long distance from thevehicle while those below the horizon get progressively closer to thevehicle in relation to the distance below the horizon in the displayedimage. Therefore, compression of the upper vertical portion of thecentral image portion may be eliminated without significant reduction inperformance.

[0075] Compression of the central image portion may also advantageouslybe provided horizontally, as well as vertically. Spatial separation ofcenter image capture device 16 from side image capture devices 14 causessimilar distortion, as that described above, in the horizontaldirection. This effect is spherical in nature and would require a morecomplex corrective action, such as compressing the image based upon theremoval of pixels from an approximation to concentric circles centeredon the center of the imaging array, or other techniques which would beapparent to those skilled in the art.

[0076] A rearview vision system 12″ includes an image display 20″ havinga compressed central image portion 48″ and left and right image portions44″ and 46″, respectively (FIG. 10). A border 50′ between left sideimage 44″ and central image 48″ includes a vertical central borderportion 50 a′, an upper border portion 50b′, and a lower border portion50 c′. Upper border portion 50 b′ and lower border portion 50 c′ divergelaterally outwardly, vertically away from central portion 50 a′. Aborder 52′ between central image portion 48″ and right image portion 46″includes a central boundary portion 52 a′, an upper boundary portion 52b′, and a lower boundary portion 52 c′. Upper boundary portion 52 b′ andlower boundary portion 52 c′ diverge laterally outwardly vertically awayfrom central portion 52 a′. This creates an upper portion of centralimage portion 48″ and a lower portion of central image portion 48″ whichextend beyond the center portion thereof. This configuration is basedupon the realization that the surface of the road immediately behind thevehicle is captured by central image capture device 16. Likewise, thehorizontal plane above the vehicle, which is symmetrical with the roadsurface, is captured by the center image capture device. This may beseen by referring to point P in FIG. 10, which illustrate the pointswhere the effective radius 68 of the virtual image capture deviceintersects dead zones 30 and by referring to point S in FIG. 10 whichillustrates the corners or the rear of the vehicle (S).

[0077] The image displayed on display 20″ includes a dead space 66′having diverging lateral sides 68 a, 68 b. Diverging sides 68 a and 68 bare configured in order to extend in the direction of travel of vehicle10 which is parallel to lane markings of a highway on which vehicle 10is travelling. This further enhances the visual perception of the driverby providing a visual clue of the location of images appearing ondisplay 20″ with respect to the vehicle 10. Side portions 68 a, 68 b, inthe illustrated embodiment, are natural extensions of lower boundaryportions 50 c′and 52 c′and extend from point S on each respective sideof the vehicle to point R, which represents the intersection of thelower extent of the vertical field of view 40 of each side image capturedevice 14 with the pavement (FIG. 7).

[0078] Rearview vision systems 12′ and 12″ utilize a displayedsynthesized image which takes into account the use of perspective inenhancing the driver's understanding of what is occurring in the areasurrounding the vehicle. The images produced on displays 20′ and 20″effectively remove the vehicle bodywork and replace the bodywork with avehicle footprint as would be viewed by virtual camera C. The imagedisplayed on display 20″ further includes perspective lines whichfurther enhance the roll of perspective in the driver's understanding ofwhat is occurring.

[0079] In order to further enhance the driver's understanding of what isoccurring in the area surrounding the vehicle, a rearview vision system12″′ includes a display 20″′ having image enhancements (FIG. 6). In theillustrative embodiment, such image enhancements include graphicoverlays 70 a, 70 b which are hash marks intended to illustrate to thedriver the anticipated path of movement of vehicle 10. In theillustrated embodiment, the anticipated vehicle motion is a function ofthe vehicle direction of travel as well as the rate of turn of thevehicle. The forward or rearward direction of vehicle travel isdetermined in response to the operator placing the gear selection device(not shown) in the reverse gear position. The degree of turn of thevehicle may be determined by monitoring the movement of the vehiclesteering system, monitoring the output of an electronic compass, ormonitoring the vehicle differential drive system. In the embodimentillustrated in FIG. 6, the configuration of graphic overlays 70 a, 70 bindicates that the vehicle is in reverse gear and that the wheels areturned in a manner that will cause the vehicle to travel toward thedriver's side of the vehicle. If the wheels were turned in the oppositedirection, graphic overlays 70 a, 70 b would curve clockwise toward theright as viewed in FIG. 6. If the vehicle's wheels were straight,graphic overlays 70 a, 70 b would be substantially straight converginglines. If the vehicle is not in reverse gear position, graphic overlays70 a, 70 b are not presented. Other types of graphic overlays of thedisplayed image are comprehended by the invention.

[0080] Horizontal grid markings on the display may be provided toindicate distances behind the vehicle at particular markings. Such gridwould allow the driver to judge the relative position of vehicles behindthe equipped vehicle. In one embodiment, short horizontal lines aresuperimposed on the displayed image at regular rearward intervals inhorizontal positions which correspond to the boundaries of the lane inwhich the vehicle is travelling. In order to avoid confusion when thevehicle is travelling in a curved path, from a lack of correspondencebetween the graphic overlay and the road, a signal indicative of thevehicle's rate of turn may be taken into account when generating thegraphic overlay. In this manner, the distance indications may be movedlaterally, with reduced horizontal separation, to correspond to thepositions of the curved lane boundaries and vertically on the image tocompensate for the difference between distances along a straight andcurved path.

[0081] Another image enhancement is to alter the appearance of an objectin a particular zone surrounding the vehicle in order to provide anindication, such as a warning, to the driver. As an example, a vehiclethat is too close to the equipped vehicle for safe-lane change, may bedisplayed in a particular color, such as red, may flash, or otherwise bedistinguishable from other images on the display. Preferably, the speedof the equipped vehicle 10, which may be obtained from known speedtransducers, may be provided as an input to the rearview vision systemin order to cause such warning to be a function of the vehicle speedwhich, in turn, affects the safe separation distance of vehicles. Theoperation of the turn signal may also be used to activate suchhighlighting of other road users or to modify the scope of the imagedisplayed. In order to determine the distance of objects behind vehicle10, a separate distance-measuring system may be used. Such separatesystem may include radar, ultrasonic sensing, infrared detection, andother known distancemeasuring systems. Alternatively, stereoscopicdistance-sensing capabilities of side image capture devices 14 may beutilized to determine the separation distance from trailing objectsutilizing known techniques.

[0082] Thus, it is seen that the image displayed on display 20-20″' maybe different under different circumstances. Such different circumstancesmay relate to the vehicle's direction of travel, speed, rate of turn,separation from adjacent objects, and the like.

[0083] Various other forms of image processing may be utilized withrearview vision system 12-12″′. Luminant and chrominant blending may beapplied to the images captured by image capture devices 14, 16 in orderto produce equality of the image data whereby the image portions appearas if they were produced by one image capture device. The dynamic rangeof the image capture devices may be extended in order to provide highquality images under all lighting conditions. Furthermore, individualpixel groups may be controlled in order to selectively compensate forbright or dark spots. For example, antiblooming techniques may beapplied for bright spots. Multiple exposure techniques may be applied tohighlight dark areas. Image morphing and warping compensation techniquesmay additionally be applied. Resolution of the image capture devices anddisplay may be selected in order to provide sufficient image quality forthe particular application.

[0084] A heater may be applied to each image capture device in order toremove dew and frost that may collect on the optics of the device.Although, in the illustrative embodiment, the optical centerline of thecamera coincides with the field of view, particular applications mayresult in the centerline of the camera pointing in a direction otherthan the centerline of the field of view. Although, in the illustrativeembodiment, the image capture devices are fixed, it may be desirable toprovide selective adjustability to the image capture devices or opticalpaths in particular applications. This is particularly desirable whenthe system is used on articulated vehicles where automated andcoordinated camera aim may be utilized to maintain completeness of thesynthesized image.

[0085] When operating the vehicle in the reverse direction, it may bedesirable to provide additional data concerning the area surrounding theimmediate rear of the vehicle. This may be accomplished by utilizingnon-symmetrical optics for the center image capture device in order toprovide a wide angle view at a lower portion of the field of view.Alternatively, a wide angle optical system could be utilized with theelectronic system selectively correcting distortion of the capturedimage. Such system would provide a distortion-free image while obtainingmore data, particularly in the area surrounding the back of the vehicle.

[0086] The invention additionally comprehends the use of more than threeimage capture devices. In addition to side image capture devicespositioned at the front sides of the vehicle and a center image capturedevice positioned at the center rear of the vehicle, additional imagecapture devices may be useful at the rear corners of the vehicle inorder to further eliminate blind spots. It may additionally be desirableto provide an additional center image capture device at a higherelevation in order to obtain data immediately behind the vehicle andthereby fill in the road surface detail immediately behind the vehicle.Such additional detail is particularly useful when operating the vehiclein the reverse direction. Of course, each of the image capture devicescould be a combination of two or more image capture devices.

[0087] Although the present invention is illustrated as used in arearview vision system, it may find utility in other applications. Forexample, the invention may be useful for providing security surveillancein an area where a building or other object obstructs the view of thearea under surveillance. Additionally, the invention may findapplication in night-vision systems and the like. For example, theinvention may be applied to forward-facing night-vision systems, orother vision enhancement systems such as may be used in adverse weatheror atmospheric conditions such as fog, applied to provide an enhanceddisplay of a synthesized image, which approximates a forward-facing viewfrom a single virtual camera located rearwardly of the driver, takingadvantage of the perspective features of the image.

[0088] A rearview vision system 150 is provided which, in addition todisplaying a rear image on display 20 which is synthesized by imageprocessor 18 from the output of image capture devices 14, 16, alsosupplies drive signals to an electrically operated optical device suchas electro-optic mirror 152, an electro-optic window 154, or both. Eventhough a panoramic view rearward of the vehicle is displayed on display20, it may be desired to provide the driver with a rearview mirror ofthe type which has conventionally been provided on vehicles. One suchmirror is an electro-optic mirror, such as an electrochromic mirror, aliquid crystal mirror, or a solenoid-operated prismatic mirror and thelike. Additionally, vehicles may be provided with electro-optic windows,such as sunroofs, rear windows, side windows, and the like, which changetransmissivity in response to a drive signal to a partial lighttransmittance level. In U.S. patent application Ser. No. 08/023,918filed Feb. 26, 1993, by Kenneth Schofield and Mark Larson for anAUTOMATIC REARVIEW MIRROR SYSTEM USING A PHOTOSENSOR ARRAY, thedisclosure of which is hereby incorporated herein by reference, atechnique is disclosed for producing a drive signal for an electricallyoperated optical device, such as an electro-optic mirror or window, fromthe image captured by a rearward-facing array. Utilizing the techniquesdisclosed therein, image processor 18 produces a drive signal on line156 in order to control the partial reflectance level of electro-opticmirror 152 and a drive signal on line 158 in order to control thepartial light transmittance level of electro-optic window 154.

[0089] A rearview vision system 160 is provided which includes a nearinfrared illumination device 162 in order to enhance an image capturedby image capture devices 14, 16 (FIG. 19). In the illustratedembodiment, infrared illumination device 162 illuminates an areaimmediately behind the vehicle. Preferably, the output of illuminationdevice 162 has a greater near infrared light output than visible lightoutput. This allows an enhanced image to be captured by the imagecapture device without increasing the visible light perceived by driverssurrounding the vehicle. Infrared illumination device 162 may beactuated in response to the vehicle being placed in reverse gear. Thisprovides backup illumination which is greatly enhanced without having anincreased effect on other drivers. Alternatively, infrared illuminationdevices may be positioned, for example, at other locations on the sideor even the front of a vehicle in order to enhance the image captured bythe image capture device or devices. This is especially useful in orderto utilize rearview vision system 160 with a large truck, such as atrailer truck. This infrared illumination device may flood the areaaround the trailer with infrared light in order to enhance the imagecaptured by the image capture device, or devices, without distractingother drivers.

[0090] Image capture device 14, 16 may include a housing 164 in which anantenna 166 is positioned. This provides a convenient and functionallocation for a receiving antenna, such as the type used with a globalpositioning system, cellular telephone, garage door opener, radardistance sensing device, and the like, as disclosed in patentapplication Serial No. 08/569,851 filed by Desmond J. O'Farrell, RogerL. Veldman and Kenneth Schofield for a VEHICLE GLOBAL POSITIONINGSYSTEM, the disclosure of which is hereby incorporated herein byreference. A heater 168 may be associated with the image capture devicein order to stabilize the temperature of the device in low ambienttemperature conditions. A similar heater may be supplied in display 20in order to improve its performance in low ambient temperatureconditions. A heater control 170 is provided in order to control theenergization of heater 168 and, if utilized, the heater in the display.Heater control 170, preferably, energizes heater 168 prior to thevehicle being started. This allows the temperature of the image capturedevice to be elevated to a more desirable temperature prior to thedriver operating the vehicle. This may be accomplished by heater control170 being a proximity detector which detects a device carried by thedriver as the driver approaches the vehicle. Alternatively, heatercontrol 170 may be responsive to a signal produced by a remote keylessentry device concurrently with the doors being activated. Alternatively,heater control 170 may be responsive to the vehicle device being opened.

[0091] A rearview vision system 172 is provided which provides anoutput, generally referred to at 174, from image processor 18 to display20. Output 174 provides an indication when an object bears apredetermined relationship to the vehicle. Such object may be ofinterest because the object is in a blind spot of the vehicle, may betailgating the vehicle, or may be an object in front of the vehiclewhich the vehicle is too close to. Display 20 may respond to output 174by highlighting the displayed vehicle, such as by displaying the vehiclein an artificial color, such as red, by flashing the image of thevehicle, or, otherwise, drawing the attention of the driver to thevehicle. Output 174 may be developed by image processor 18 from theoutputs of image capture devices 14, 16. This may be accomplished by,for example, utilizing redundant image portions captured by the imagecapture devices, even though not displayed by display 20, in order tocalculate relative position of the object with respect to the vehicle.Alternatively, an object sensor 176 may be provided in order to supplyan output 178 indicative of a predetermined positional relationship ofan object sensed by the object sensor with respect to the vehicle. Inthe illustrated embodiment, object sensor 176 may be a passive infraredsensor which senses the presence of an object in the vehicle's blindspot. Alternatively, object sensor 176 may be a distance-measuringdevice, such as an active infrared sensor, an ultrasonic sensor, a radarsensor, or the like. Such object sensor is especially useful indetermining the separation distance between the vehicle and objects infront of the vehicle. Preferably, object sensor 176 has a sensing fieldof view that is substantially coincident with the field of view of oneor more of the image capture devices 14, 16.

[0092] A rearview vision system 178 is provided which has the capabilityof displaying stereoscopic images rearward of the vehicle. Rearviewvision system 178 includes at least one pair of image capture devices14a, which are closely positioned on the vehicle and have overlappingfields of view. Because the image capture device pairs are closelypositioned, they capture substantially the same image but from aslightly different angle. This allows image processor 18 to produce avideo signal 100′ with stereoscopic information. This signal is utilizedby a stereoscopic display 320 in order to produce a stereoscopic imagerearward of the vehicle. Such stereoscopic displays are known in theart. Although one pair of image capture devices are illustrated in FIG.22, rearview vision system 178 may include multiple pairs of imagecapture devices. This allows a rear image to be synthesized from themultiple pairs of image capture devices in order produce a panoramicview rearward of the vehicle and stereoscopic image. Preferably,utilizing other aspects of the invention, the stereoscopic image is arearward-facing view from a single location.

[0093] A rearview vision system 180 is provided which produces anindication 182 of road line markings. Indication 182 may also indicateroad edges. Image processor 18 detects the road line markings and theroad edges from the images captured by image capture devices 14, 16.This feature may be further enhanced by combining it with an infraredillumination device 162 in order to further illuminate areas behind andaround the vehicle in order to enhance the image of the road linemarkings and the road edges. Indication 182 may be utilized by display20 in order to provide an indication of the vehicle with respect to theroad line markings and road edges. The indication may further beutilized by an indicator which indicates the relative position of thevehicle in its lane. Additionally, the indication may be utilized todetermine erotic vehicle operation, such as may occur when the driverbegins to fall asleep, in order to provide a suitable alarm, or thelike.

[0094] A rearview vision system 184 is provided with capabilities forinfrared communication with other vehicles and stationary beacons.Rearview vision system 184 produces a communication data output 186which includes communication data decoded from infrared signals detectedby image capture device or devices 14, 16. For example, suitablestandards may be developed wherein vehicles are equipped with a pair ofspaced apart infrared transmitters on a forward portion thereof. Imageprocessor 18 may respond to the temporal and spatial patterns ofinfrared signals detected by image capture devices 14, 16 in order todetermine the speed and distance and, thereby, the separation of thevehicles as well as the rate of change of separation of the vehicles.Such information may be communicated to the trailing vehicle by aninfrared transmitter (not shown) in order to control the speed of thetrailing vehicle. This feature provides adaptive cruise control in whichthe speed of the trailing vehicle is controlled according to separationdistance with leading vehicles. This allows high-speed convoying betweenvehicles. The communication system may additionally provide for theidentification of emergency vehicles, and the like, which may transmit aunique temporal and/or spatial pattern of an infrared signal. The IRcommunication signal may additionally be utilized to receive signalsfrom stationary devices, such as location beacons and IntelligentVehicle Highway System (IVHS) data. Because rearview vision system 184has a field of view which extends generally rearwardly of the vehicle,the system provides the capability for sensing information after thevehicle has passed the beacon. This provides an adjunct to infraredcommunication systems having a field of view generally forward of, or tothe side of, the vehicle.

[0095] A rearview vision system 188 is provided having extended dynamicrange (FIG. 25). Rearview vision system 188 includes a pair of imagecapture devices 14 and/or 16, each of which has an image-sensing array190. Each image capture device is capable of operating in either a colormode, in which a color image is displayed on display 20, or a monochromemode, in which a monochrome image is displayed on display 20. System 188includes an image luminance sensor 192 which senses the luminance levelof images captured by image capture devices 14, 16. Image luminancesensor 192 may switch the image capture devices between the color modeand the monochrome mode such that, when the image luminance issufficiently high, the image capture device, or devices, operate in acolor mode. During low image luminance conditions, the image capturedevice, or devices, are operated in a monochromatic mode which does notrequire as much image luminance. This extends the dynamic range of thesystem. Rearview vision system 188 may additionally include an exposurecontrol 194 which determines the exposure period for capturing eachframe by arrays 190. In order to extend the dynamic range of system 188,exposure control 194 may produce exposure intervals for arrays 190 whichvary in length from interval-to-interval. Thus, a series of normalexposure intervals may be occasionally supplanted by a longer exposureinterval during which greater detail of the image may be captured. Thisenhanced image may then be combined with the image captured during theshorter intervals into a merged image of enhanced detail.

[0096] Rearview vision system 188 may additionally include a pluralityof infrared shutters 196 which are in the optical paths 198 of arrays190. Each infrared shutter 196 has at least one state in which infraredenergy is generally not attenuated to array 190. In another state, theinfrared shutter generally blocks infrared radiation from the array. Thestate of infrared shutters 196 is controlled by image luminance sensor192. During periods of high image luminance, sensor 192 may switch theinfrared shutters 196 to a state blocking near infrared radiation fromarrays 190. However, during low image luminance conditions, sensor 198may switch the infrared shutters 196 to a state in which the nearinfrared energy is transmitted to arrays 190. The addition of the nearinfrared radiation at low luminance levels enhances the image luminancesensed by arrays 190. In the illustrated embodiment, infrared shutters196 are either electrochromic shutters or liquid crystal shutters, bothof which are known in the art. Rearview vision system 188 additionallyincludes means for coordinating the image intensity received frommultiple image capture devices and displayed on display 20. This allowsa balance composite image to be displayed on the display. This may beprovided by a display intensity control 200 which regulates theintensity of the output of both arrays 190 in order to produce color andluminance balancing between the multiple image capture devices. Insteadof a separate display intensity control, a direct communication channelmay be developed between the image capture devices in order to providecolor and luminance balancing.

[0097] Each image pixel captured by image capture devices 14, 16 anddisplayed on display 20 has a resolution which affects the amount ofimage detail displayed. While it is desirable to have a high degree ofdetail of displayed image, the increase in image resolution produces acommensurate increase in system cost. While it is desirable to reducesystem cost, this should not be achieved by sacrificing necessary detailin the displayed image. According to the invention, it has beendetermined that sufficient image detail may be obtained at a suitablesystem cost by having a pixel resolution in the range of betweenapproximately 2 arc minutes and approximately 8 arc minutes. Preferably,system resolution is approximately 6 arc minutes.

[0098] It is known in the art to provide imaging array capture deviceshaving mosaic filters which mask image radiation in order to producepixels which respond respectively to red, green, and blue light. Becausesuch known pixel filter masks do not adequately absorb near infraredradiation, it is known to supply infrared filters in order to blockinfrared radiation from the pixels so that the pixels respond to onlythe designed radiation band. However, such additional filters haveundesirable characteristics including costs. It has been discovered thata pixel filter mask may be made responsive to red, green, or blue lightwhile filtering out near infrared by adding appropriate dyes to the dyesmaking up the filter mask.

[0099] The heater supplied with each image capture device may include atransparent conductive coating applied to a window covering the devicelens. Alternative heater constructions include ITO or a series of finewire mesh. This provides protection of the lens of the image capturedevice from physical harm while allowing moisture and frost to beremoved from the window.

[0100] Various manipulation techniques may be applied to image capturedevices 14, 16. For example, when the invention is applied tosemi-tractor/trailer combinations, the image capture devices may bemotorized and responsive to signals representing the relative positionof the trailer and the cab in order to produce full panoramic viewduring various maneuvers of the vehicle. For example, as the vehicleturns, which may cause the trailer to otherwise block the image capturedby a side image capture device, the image capture device may pivot to adifferent panoramic view which is not blocked by the trailer.Additionally, the panoramic view sensed by the image capture device maybe different when the trailer is attached than when the trailer is notattached. In a similar fashion, rearward-mounted image capture device 16may be motorized to move vertically upwardly and downwardly between afirst position when the vehicle is moving in a forward direction and asecond position when the vehicle is in reverse gear. In the secondposition, the motorized camera is directed more downwardly in order tocapture images closer to the rear of the vehicle which may be contactedby the vehicle. Image capture devices 14, 16 may be supplied withelectrical opto-mechanical zoom devices as well as vibration isolationand compensation stabilizing devices.

[0101] Image processor 18 may provide an input to a control for theintensity of the brake lights, turn signals, and the like for thevehicle. In this manner, the image processor may control the intensityof such lights based upon ambient lighting conditions. This allows theintensity of the rearward directed lights to be less distracting forfollowing vehicles.

[0102] Additionally, the present invention may be utilized for providingguidance for a tractor/trailer or like vehicle backing to a loadingdock. Additionally, the invention may provide guidance for properalignment of the trailer and tractor which are being joined by backingof the tractor. The present invention may additionally provide accidentmonitoring by capturing a predetermined continuous stream of images,such as, for example, 15 seconds. This running store of image may befrozen upon impact of the vehicle, in order to record events leading upto the impact, or may be stopped by a manual input. Furthermore, theinvention may be utilized to alert the driver to an impending rear-endcollision. The vehicle may respond to such indication by deploying anappropriate device, such as a smart headrest or the like.

[0103] Thus, it is seen that the present invention enhances therelationship between the driver's primary view and the image presentedon the rearview vision system. This is accomplished in a manner whichprovides ease of interpretation while avoiding confusion so that thedriver does not have to concentrate or look closely at the image. Inthis manner, information presented on the display is naturallyassimilated. This is accomplished while reducing blind spots so thatother vehicles or objects of interest to the driver will likely bedisplayed to the driver. Additionally, the use of perspective allowsdistances to be more accurately determined.

[0104] Changes and modifications in the specifically describedembodiments can be carried out without departing from the principles ofthe invention, which is intended to be limited only by the scope of theappended claims, as interpreted according to the principles of patentlaw including the doctrine of equivalents.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defied as follows: 1 A rearview vision systemfor a vehicle, comprising: at least two image capture devices positionedon the vehicle and directed rearwardly with respect to the direction oftravel of said vehicle; and a display system which displays an imagesynthesized from outputs of said image capture devices and whichapproximates a rearward-facing substantially seamless panoramic viewfrom a single location substantially without duplicate redundant imagesof objects.
 2. The rearview vision system in claim 1 wherein said singlelocation is forward of the driver with respect to said direction oftravel and said rearward-facing view is unobstructed by the vehicle. 3The rearview vision system in claim 1 wherein said image capture devicesare spatially separated. 4 The rearview vision system in claim 1 whereinthe displayed image includes a visual prompt of the location of saidvehicle in said view 5
 5. The rearview vision system in claim 4 whereinsaid visual prompt is an outline of an area which would substantially beoccupied by said vehicle in said view. 6 The rearview vision system inclaim 4 wherein said visual prompt includes perspective lines which arealigned with said direction of travel
 7. 7. The rearview vision systemof claim 1 wherein said at least two image capture devices comprises atleast three image capture devices. 8 The rearview vision system in claim7 wherein said at least three image capture devices include at least twoside image capture devices positioned on opposite lateral sides of saidvehicle and at least one center image capture device laterally betweensaid side image capture devices.
 9. The rearview vision system in claim7 wherein said at least three image capture devices are at substantiallythe same height.
 10. The rearview vision system in claim 7 wherein saidat least three image capture devices are aimed along non-parallel axes.11. The rearview vision system in claim 8 wherein the displayed imageincludes an image portion from each of said image capture devices andwherein said image portion from said center image capture device has avertically central portion and vertically upper and lower portions,wherein said upper and lower portions are laterally wider than the saidcentral portion.
 12. The rearview vision system in claim 8 wherein thedisplayed image includes an image portion from each of said imagecapture devices and wherein said image portion from said center imagecapture device is compressed.
 13. The rearview vision system in claim 8wherein the displayed image includes an image portion from each of saidimage capture devices and wherein each of said image portions has ahorizontal field of view that is less than 70 degrees.
 14. The rearviewvision system in claim 13 wherein said horizontal field of view of saidcenter image portion from said center capture device is less thanapproximately 12 degrees.
 15. The rearview vision system in claim 14wherein said horizontal field of view of said image portion from saidcenter image capture device is between approximately 3 degrees andapproximately 8 degrees.
 16. The rearview vision system in claim 1wherein said display system includes multiple contiguous displaysurfaces one of said surfaces for each of said images.
 17. The rearviewvision system in claim 1 wherein said display system includes a displaysurface for displaying all of said images.
 18. The rearview visionsystem in claim 1 wherein each of said image capture devices is a CMOSimaging array.
 19. The rearview vision system in claim 8 wherein thedisplayed image includes an image portion from said center image capturedevice which has a horizontal width that is narrower than the horizontalwidth of image portions from said side image capture devices. 20 Therearview vision system in claim 19 wherein said horizontal width of saidimage portion from said center image capture device is dynamicallyadjustable.
 21. The rearview vision system in claim 20 wherein saidhorizontal width of said image portion from said center image capturedevice is adjustable in response to vehicle speed.
 22. A rearview visionsystem for a vehicle, comprising: at least three image capture devicesmounted to the vehicle and directed rearwardly with respect to thedirection of travel of said vehicle. at least two of said image capturedevices being side image capture devices respectively mounted onopposite lateral sides of said vehicle and at least one of said imagecapture devices being a center image capture device mounted between saidside image capture devices wherein said side image capture devices andsaid center image capture device capture objects rearwardly of thevehicle from different angles; and a display system which displays animage synthesized from outputs of said image capture devices, thedisplayed image including image portions from each of said image capturedevices combined at boundaries; wherein the image portion from saidcenter image capture devices includes a portion which is compressedthereby reducing image disjointment at said boundaries.
 23. Thc rearviewvision system in claim 22 wherein said portion of said image portionfrom said center image capture device is vertically compressed.
 24. Therearview vision system in claim 23 wherein said image portion from saidcenter image capture device is made up of a plurality of horizontallines and wherein said portion of said image portion is compressed bydeleting particular ones of said horizontal lines.
 25. The rearviewvision system in claim 24 wherein a greater number of said horizontallines are removed further away from a vertical center of said imageportion from said center image capture device.
 26. The rearview visionsystem in claim 24 including adjusting values of adjacent pixels as afunction of pixel values of removed ones of said horizontal lines. 27.The rearview vision system in claim 22 wherein said image portion fromsaid center image capture device has a vertically central portion andvertically upper and lower portions, wherein said upper and lowerportions are laterally wider than said central portion.
 28. The rearviewvision system in claim 22 including a visual prompt of the vehiclevertically below said image portion from said center image capturedevice.
 29. The rearview vision system in claim 28 wherein said visualprompt is an outline of an area which would substantially be occupied bysaid vehicle in said displayed image.
 30. The rearview vision system inclaim 28 wherein said visual prompt includes perspective lines which arealigned with said direction of travel.
 31. The rearview vision system inclaim 22 wherein said display system includes multiple contiguousdisplay surfaces, one of said surfaces for each of said image portions.32. The rearview vision system in claim 22 wherein said display systemincludes a display surface for displaying all of said image portions.33. The rearview vision system in claim 22 wherein each of said imagecapture devices Is a CMOS imaging array.
 34. The rearview vision systemin claim 22 wherein said at least three image capture devices are atsubstantially the same height on the vehicle.
 35. The rearview visionsystem in claim 22 wherein said at least three image capture devices areaimed along nonparallel horizontal axes.
 36. A rearview vision systemfor a vehicle having a gear actuator, comprising: at least two imagecapture devices positioned on the vehicle and directed rearwardly withrespect to the direction of forward travel of said vehicle; a displaysystem which displays an image synthesized from outputs of said imagecapture devices; and said display system producing a graphic overlaysuperimposed on said displayed image visible to the driver informing thedriver of what is occurring in the area surrounding the vehicle.
 37. Therearview vision system in claim 36 wherein said graphic overlay is inthe form of indicia of the anticipated path of travel of the vehicle.38. The rearview vision system in claim 37 wherein said graphic overlayis disabled when the vehicle's gear actuator is not in reverse gear. 39.The rearview vision system in claim 38 wherein said indicia has a formthat responds to the rate of turn of the vehicle.
 40. The rearviewvision system in claim 39 wherein said indicia form responds to at leastone of the vehicle's steering system, the vehicle's differential system,and a compass.
 41. The rearview vision system in claim 36 wherein saidgraphic overlay has a form that is a function of at least one of thedirection or travel and speed of the vehicle.
 42. The rearview visionsystem in claim 36 wherein said graphic overlay is a distance indiciaindicating distances behind the vehicle of objects.
 43. The rearviewvision system in claim 42 wherein said indicia has a form that respondsto the rate of turn of the vehicle
 44. The rearview vision system inclaim 43 wherein said indicia form responds to at least one of thevehicle's steering system, the vehicle's differential system, and acompass.
 45. The rearview vision system in claim 36 wherein said atleast one image capture device includes a plurality of image capturedevices and wherein the displayed image is synthesized from outputs ofsaid image capture devices and approximates a rearward-facing view froma single location.
 46. The rearview vision system in claim 45 whereinsaid single location is forward of the driver with respect to saiddirection of travel.
 47. The rearview vision system in claim 36 whereinthe displayed image includes a visual prompt of the location of saidvehicle in said view.
 48. The rearview vision system in claim 47 whereinsaid visual prompt is an outline of an area which would substantially beoccupied by said vehicle in said view.
 49. The rearview vision system inclaim 47 wherein said visual prompt includes perspective lines which arealigned with said direction of travel.
 50. A rearview vision system fora vehicle, comprising: at least one image capture device positioned onthe vehicle and directed generally rearwardly with respect To thedirection of travel of the vehicle; and a display system displaying arear image synthesized from output of said at least one image capturedevice substantially contiguous with the forward field of view of thevehicle driver at a focal length that is forward of the vehiclepassenger compartment.
 51. The rearview vision system in claim 50wherein said display system displays an image at a focal length that iswithin the depth of field of a vehicle driver viewing a distant object.52. The rearview vision system in claim 50 wherein said display systemdisplays an image either generally above or generally below the centralforward field of view of the vehicle driver.
 53. The rearview visionsystem in claim 50 wherein said display system includes an opaqueviewing portion which blocks view of near field objects located betweenthe forward field of view of the vehicle driver and the displayed image.54. The rearview vision system in claim 50 wherein said display systemdefines an observation cone within which an image displayed by thedisplay system can be observed and further including accommodating meansfor accommodating variation in relationship between a driver's head andsaid observation cone.
 55. The rearview vision system in claim 54wherein said accommodating means includes adjustment means for adjustingsaid observation cone in at least one of a horizontal and a verticaldirection.
 56. The rearview vision system in claim 54 wherein saidaccommodating means includes establishing the rearward field of viewcaptured by said capture device and displayed on said display systembeyond that normally observed by a driver.
 57. The rearview visionsystem in claim 50 wherein said display system defines an observationcone within which an image displayed by the display system can beobserved, wherein said observation cone is adjustable in at least one ofa horizontal and a vertical direction.
 58. The rearview vision system inclaim 57 including an adjustment mechanism which adjusts saidobservation cone in said at least one of a horizontal and a verticaldirection.
 59. The rearview vision system in claim 58 wherein saidadjustment mechanism includes an electrically operated actuator which iscontrollable by a driver-operable switch.
 60. The rearview vision systemin claim 50 wherein said display system has a variable luminance outputwhich is varied as a function of ambient light levels.
 61. The rearviewvision system in claim 60 wherein the luminance output of said displaysystem is responsive to one of a vehicle headlight activation control,an ambient light sensor, and an indication of ambient light leveldeveloped by said at least one image capture device.
 62. The rearviewvision system in claim 60 wherein said display system includes a usercomfort level setting to establish a desired luminance output level at aparticular ambient light level.
 63. The rearview vision system in claim50 wherein said display system includes an image generator and an imagemagnifier which magnifies an image generated by said image generator.64. The rearview vision system in claim 50 wherein said display deviceis an opaque display.
 65. The rearview vision system in claim 64 whereinsaid opaque display is in-line with the generally forward field of viewof the vehicle driver.
 66. The rearview vision system in claim 64wherein said opaque display is at an angle with the generally forwardfield of view of the driver and directed toward the vehicle driver'sgenerally forward field of view by a reflection device.
 67. The rearviewvision system in claim 50 wherein said display device is a view-throughheads-up display which projects an image on an image combiner whichcombines the projected image with an image forward of the vehicle. 68.The rearview vision system in claim 67 wherein said image combinerincludes a surface of a vehicle windshield.
 69. The rearview visionsystem in claim 67 wherein said display device combines an image of apolygon with the rear image in order to border the rear image anddifferentiate the rear image from an image forward of the vehicle. 70.The rearview vision system in claim 50 wherein said at least one imagecapture device includes at least two image capture devices and whereinsaid display system displays an image synthesized from outputs of saidat least two image capture devices which approximates a rearward-facingview from a single location.
 71. The rearview vision system in claim 70wherein the rear image displayed by said display system has an aspectratio that is between approximately 4:1 and approximately 2:1.
 72. Therearview vision system in claim 71 wherein the rear image displayed bysaid display system has an aspect ratio that is approximately 8:3. 73.The rearview vision system in claim 72 wherein said display system alsodisplays a supplemental image.
 74. The rearview vision system in claim73 wherein said display system is reconfigurable in order to selectivelydisplay different supplemental images.
 75. The rearview vision system inclaim 73 wherein said supplemental image includes at least one of pagerinformation, telephone number listing, global positioning system output,map, route guidance information, intelligent vehicle highway systeminformation, vehicle radio control settings, vehicle environmentalsystem settings, vehicle speed, vehicle heading, and turn signalindicators.
 76. The rearview vision system in claim 50 wherein saiddisplay system also displays a supplemental image.
 77. The rearviewvision system in claim 76 wherein said display system is reconfigurablein order to selectively display different supplemental images.
 78. Therearview vision system in claim 76 wherein said supplemental imageincludes at least one of pager information, telephone number listing,global positioning system output, map, route guidance information,intelligent vehicle highway system information, vehicle radio controlsettings, vehicle environmental system settings, vehicle speed, vehicleheading, and turn signal indicators.
 79. The rearview vision system inclaim 50 wherein the rear image displayed by said display system has anaspect ratio that is between approximately 4:1 and 2:1.
 80. The rearviewvision system in claim 79 wherein the rear image displayed by saiddisplay system has an aspect ratio that is approximately 8:3.
 81. Therearview vision system in claim 53 wherein said housing includes a bezelaround at least a portion of the displayed image, wherein said bezel hasa narrow portion adjacent the forward field of view of the vehicledriver.
 82. A rearview vision system for a vehicle, comprising: at leastone image capture device positioned on the vehicle and directedgenerally rearwardly with respect to the direction of travel of thevehicle; and a display system displaying a rear image captured by saidat least one image capture device, wherein said rear image displayed bysaid display system is a unitary image having an aspect ratio that isbetween approximately 4:1 and approximately 2:1.
 83. The rearview visionsystem in claim 82 wherein the rear image displayed by said displaysystem has an aspect ratio that is approximately 8:3.
 84. The rearviewvision system in claim 82 wherein said display system also displays asupplemental image.
 85. The rearview vision system in claim 84 whereindisplay system is reconfigurable in order to selectively displaydifferent supplemental images.
 86. The rearview vision system in claim84 wherein said supplemental image includes at least one of pagerinformation, telephone number listing, global positioning system output,map, route guidance information, intelligent vehicle highway systeminformation, vehicle radio control settings, vehicle environmentalsystem settings, vehicle speed, vehicle heading, and turn signalindicators.
 87. The rearview vision system in claim 82 wherein said atleast one image capture device includes a plurality of image capturedevices and wherein the rear image is synthesized from a plurality ofimages captured by said plurality of image capture devices whichapproximates a rearward-facing view from a single location.
 88. Arearview vision system for a vehicle, comprising: at least one imagecapture device positioned on the vehicle and directed generallyrearwardly with respect to the direction of travel of said vehicle; anda display system which displays an image synthesized from output of saidat least one image capture device as a unitary image; wherein saiddisplay system includes at least one image generator associated withsaid at least one image capture device and an optical correction systemwhich amplifies image generated by said image generator to increase thefocal lengths of the image generated by the image generator.
 89. Therear vision system in claim 88 wherein said display device is aview-through heads-up display which projects an image on an imagecombiner which combines the projected image with an image forward of thevehicle.
 90. The rearview vision system in claim 89 wherein said imagecombiner includes a surface of a vehicle windshield.
 91. The rearviewvision system in claim 89 wherein said display device combines an imageof a polygon with the rear image in order to border the rear image anddifferentiate the rear image from an image forward of the vehicle. 92.The rearview vision system in claim 83 wherein said display system is anopaque display.
 93. The rearview vision system in claim 92 wherein saidopaque display is in-line with the generally forward field of view ofthe vehicle driver.
 94. The rearview vision system in claim 92 whereinsaid opaque display is at an angle with the generally forward field ofview of the driver and directed toward the vehicle driver's generallyforward field of view by a reflection device.
 95. The rearview visionsystem in claim 92 wherein said display displays said rear imagesubstantially contiguous with the forward field of view of the vehicledriver.
 96. The rearview vision system in claim 95 wherein said displaydisplays said rear image laterally substantially directly forward of thevehicle driver.
 97. The rearview vision system in claim 95 wherein saiddisplay displays said rear image positioned either above or below thecentral forward field of view of the vehicle driver.
 98. The rearviewvision system in claim 92 wherein a portion of said display blocks theview of near field objects between the vehicle driver's forward field ofview and said display.
 99. The rearview vision system in claim 88wherein said display system defines an observation cone within which animage displayed by the display system can be observed and furtherincluding accommodating means for accommodating variation inrelationship between a driver's head and said observation cone.
 100. Therearview vision system in claim 99 wherein said accommodating meansincludes adjustment means for adjusting said observation cone in atleast one of a horizontal and a vertical direction.
 101. The rearviewvision system in claim 99 wherein said accommodating means includes saidimage generator establishing the rearward field of view captured by saidcapture device and displayed on said display system beyond that normallyobserved by a driver.
 102. The rearview vision system in claim 88wherein said display system defines an observation cone within which animage displayed by the display system can be observed, wherein saidobservation cone is adjustable in at least one of a horizontal and avertical direction.
 103. The rearview vision system in claim 102including an adjustment mechanism which adjusts said observation cone insaid at least one of a horizontal and a vertical direction.
 104. Therearview vision system in claim 103 wherein said adjustment mechanismincludes an electrically operated actuator which is controllable by adriver-operable switch.
 105. The rearview vision system in claim 88wherein said display system has a variable luminance output which isvaried as a function of ambient light levels.
 106. The rearview visionsystem in claim 105 wherein the luminance output of said display systemis responsive to one of a vehicle headlight activation control, anambient light sensor, and an indication of ambient light level developedby said at least one image capture device.
 107. The rearview visionsystem in claim 105 wherein said display system includes a user comfortlevel to establish a desired luminance output level at a particularambient light level.
 108. The rearview vision system in claim 88including a plurality of image capture devices and a plurality of imagegenerators, each associated with one or more of said image capturedevices and wherein said optical correction system merges imagescaptured by said image capture device.
 109. A rearview vision system fora vehicle, comprising: at least one image capture device positioned onthe vehicle and directed generally rearwardly with respect to thedirection of travel of the vehicle; a display system displaying a rearimage synthesized from output of said at least one image capture device;and an electrically operated optical device which is responsive to adrive signal in order to have a partial light transmission level;wherein said drive signal is produced from said output of said at leastone image capture device.
 110. The rearview vision system in claim 109wherein said electrically operated optical device is at least one of anelectro-optic rearview mirror, an electro-optic window and a prismaticrearview mirror.
 111. A rearview vision system for a vehicle,comprising: at least one image capture device positioned on the vehicleand directed generally rearwardly with respect to the direction oftravel of the vehicle; a display system displaying a rear imagesynthesized from output of said at least one image capture device; and anear infrared illumination device positioned to illuminate an areaoutside of the vehicle in order to enhance an image captured by said atleast one image capture device.
 112. The rearview vision system in claim111 wherein said illumination device produces substantially greaterinfrared light output than visible light output.
 113. The rearviewvision system in claim 112 wherein said illumination device is actuatedin response to the vehicle being placed in reverse gear.
 114. Therearview vision system in claim 112 wherein said illumination devicefloods areas around a trailer of a truck.
 115. A rearview vision systemfor a vehicle, comprising: at least one image capture device positionedon the vehicle and directed generally rearwardly with respect to thedirection of travel of the vehicle; a display system displaying a rearimage synthesized from output of said at least one image capture device;a housing for said image capture device; and an antenna positioned insaid housing in order to receive electromagnetic radiation of aparticular characteristic.
 116. The rearview vision system in claim 115wherein said antenna is one of a global positioning system antenna, acellular telephone antenna, a radar antenna, and a garage door openerantenna.
 117. A rearview vision system for a vehicle, comprising: atleast one image capture device positioned on the vehicle and directedgenerally rearwardly with respect to the direction of travel of thevehicle; a display system displaying a rear image synthesized fromoutput of said at least one image capture device; and designation meansfor measuring the distance of objects from the vehicle and indicatingobjects which have a predetermined positional relationship to thevehicle.
 118. The rearview vision system in claim 117 wherein saiddesignation means includes a distance measuring device.
 119. Therearview vision system in claim 117 wherein said distance measuringdevice is one of a passive infrared sensor, a radar sensor, an activeinfrared sensor and an ultrasonic sensor.
 120. The rearview visionsystem in claim 119 wherein said distance measuring device has a sensingfield of view that is substantially coincident with the field of view ofsaid image capture device.
 121. The rearview vision system in claim 117wherein said designation means produces an indication on said rear imageof objects which have a predetermined positional relationship to thevehicle.
 122. A rearview vision system for a vehicle, comprising: atleast two image capture devices closely positioned on the vehicle withat least partially overlapping fields of view and directed generallyrearwardly with respect to the direction of travel of the vehicle; and astereoscopic display system displaying a stereoscopic rear imagesynthesized from outputs of said at least two image capture devices.123. The rearview vision system for a vehicle wherein said at least twoimage capture devices includes multiple pairs of image capture deviceswith at least partially overlapping fields of view in each pair andwherein said display system displays a rear image synthesized fromoutputs of said multiple pairs of image capture devices whichapproximates a rearward-facing view from a single location.
 124. Arearview vision system for a vehicle, comprising: at least one imagecapture device positioned on the vehicle and directed generallyrearwardly with respect to the direction of travel of the vehicle; adisplay system displaying a rear image synthesized from output of saidat least one image capture device; and means responsive to said outputfor detecting road lane markings rearward of the vehicle.
 125. Therearview vision system in claim 124 wherein said display system displaysa position of the vehicle with respect to the detected road lanemarkings.
 126. The rearview vision system in claim 124 including adriver alertness warning which is responsive to the position of thevehicle with respect to the detected road lane markings.
 127. Therearview vision system in claim 124 including an infrared light sourcefor illuminating a portion of a road rearward of the vehicle.
 128. Therearview vision system in claim 124 including a forward-facing road lanemarking detector.
 129. A rearview vision system for a vehicle,comprising: at least one image capture device positioned on the vehicleand directed generally rearwardly with respect to the direction oftravel of the vehicle; a display system displaying a rear imagesynthesized from output of said at least one image capture device; andan infrared communication channel defined from said output whichreceives communications external of the vehicle.
 130. The rearviewvision system in claim 129 wherein said infrared communication channelis responsive to at least one of a temporal and a spatial pattern of aninfrared signal.
 131. The rearview vision system in claim 130 whereinsaid infrared communication channel determines at least one of relativespeed and distance between the source of an infrared signal and thevehicle.
 132. The rearview vision system in claim 129 wherein saidinfrared communication channel is responsive to infrared signalsreceived from one of a stationary source and a source on anothervehicle.
 133. A rearview vision system for a vehicle, comprising: atleast one image capture device positioned on the vehicle and directedgenerally rearwardly with respect to the direction of travel of thevehicle; a display system displaying a rear image synthesized fromoutput of said at least one image capture device; and an interfacebetween said output and said display device which synchronously mapsimage pixels from said output to said display system.
 134. The rearviewvision system in claim 133 wherein said interface transmits pixel datawhich represents changes in the captured image.
 135. The rearview visionsystem in claim 134 wherein said pixel data which represents changes inthe captured image includes image data and pixel position data.
 136. Arearview vision system for a vehicle, comprising: at least one imagecapture device positioned on the vehicle and directed generallyrearwardly with respect to the direction of travel of the vehicle; and adisplay system displaying a rear image synthesized from output of saidat least one image capture device; wherein said at least one imagecapture device includes an extended dynamic range to respond tovariations in image illumination.
 137. The rearview vision system inclaim 136 wherein said image capture device is capable of operating inone of a color mode and a monochrome mode and wherein said extendeddynamic range is achieved by changing between said modes in response toimage illumination conditions.
 138. The rearview vision system in claim136 wherein said image capture device captures an image during anexposure interval and wherein said extended dynamic range is achieved bycombining exposure intervals of different lengths.
 139. The rearviewvision system in claim 136 wherein said image capture device includes aninfrared shutter which is selectively operable to generally passinfrared radiation during low image illumination conditions and blockinfrared radiation during high image illumination conditions.
 140. Therearview vision system in claim 139 wherein said infrared shutter is oneof an electrochromic shutter and a liquid crystal shutter.
 141. Therearview vision system in claim 136 including a plurality of imagecapture devices and including image intensity coordination between saidimage capture devices.
 142. A rearview vision system for a vehicle,comprising: at least one image capture device positioned on the vehicleand directed generally rearwardly with respect to the direction oftravel of the vehicle; a display system displaying a rear imagesynthesized from output of said at least one image capture device; aheater in at least one of said image capture device and said displaysystem; and a control which energizes said heater during low temperatureconditions prior to starting the vehicle.
 143. The rearview visionsystem in claim 142 wherein said control includes at least one of aproximity sensor to sense a user approaching the vehicle and a remotekeyless entry sensor responsive to a remote keyless entry signal. 144.The rearview vision system in claim 142 including a heater in both saidimage capture device and said display system.
 145. A rearview visionsystem for a vehicle, comprising: at least one image capture devicepositioned on the vehicle and directed generally rearwardly with respectto the direction of travel of the vehicle; and a display systemdisplaying a rear image synthesized from output of said at least oneimage capture device; wherein said rear image has a pixel resolution inthe range of between approximately 2 arc-minutes and approximately 8arc-minutes.
 146. The rearview vision system in claim 145 wherein saidresolution is approximately 6 arc-minutes.
 147. The rearview visionsystem in claim 145 including a plurality of image capture devices andwherein said resolution is divided between said image capture devices.